Electron device and method of operating



A. w. HULL ELECTRON DEVTCE AND METHOD OF OPERATING HEAT/N6 CURRENT FiledNov. 15, 1921 Fig. 4.

F12. 5. CUR/TEN T VOLT/16E 0F H/Gh' THRU F/LAMENT TENS/0N Ll/VEInventor: Albert w. HUN, by Maw; His.v Attorney.

Patented Jan. 20, 1925.

UNITED STATES PATENT OFFICE.

ALBERT W. HULL, OF SCHENECTADY, NEW YORK, ASSIGNOR TO COMPANY, ACORPORATION OF NEW YORK.

GENERAL ELECTRIC ELECTRON DEVICE AND METHOD OF OPERATING.

Application filed November 15, 1921.

To alt whom it mag concern.

Be it known that I, ALBERT W. HULL, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in ElectronDevices and Methods of Operating, of which the following is aspecification.

The present invention comprises an improved electrical device belongingto the general class of devices known as magnetrons, which are describedby me in the Journal of the American Institute of Electrical Engineers,Septen'iber, 1921, Vol. XLI, page (327. v

A magnetron comprises an electron-emitting cathode and an anode arrangedin such relation to each other that a current between these electrodesmay be varied or interrupted by a suitably applied magnetic field. Forexample, the cathode may consist of a simple linear filament and theanode consist of a conducting cylinder symmetrically arranged about thecathode filament. In magnetrons now being used as radio detectors thecontrolling magnetic field is parallel to the cathode and is generatedby an electrical winding surrounding the magnetron tube. Assuming agiven voltage to be applied to the cathode and anode and the magneticfield value to be progressively increased from zero, the electron orspace current in the tube at first is substantially unaffected over arange of field values; then as the magnetic field exceeds a critical'alue, depending on the characteristics of a particular device. and theapplied voltage, the electron current rapidly decreases, and finallywith a sufliciently high field value the electron current becomes zero.

plied will overcome the deflection force of' the current ordinarilyrequired to render incandescent a filament of this size. When theapplied voltage is as low as about one Volt, the heating current in afilament of seven Serial No. 515,410.

mils diameter is sufiicient to produce an appreciable decrease ofelectron current, by what 1 term an axial magneto-strictive effect. lheterm magneto-strictive effect may be used in a broad sense to refer tothe limitation of an electron current by a magnetic field. An axialmagneto-strictive eifect in a more restricted sense designates thecontrolling efi'ect upon an electron current exerted by a magneticfield, the lines .of force of which are oriented in planes substantiallyat right angles to the axis of the device. In a device in which an axialmagneto-strictive effect is exerted by a current flowing through one oftwosubstantially parallel conductors, the control of the current isproduced by the bending of the paths of the electrons by the magneticfield so that the electrons emitted by one electrode fail to reach thesecond electrode. In the case of concentric conductors and in theabsence of any other magnetic field the paths of these electrons will bein planes passing through the axis of the current carrying conductor. Ingeneral, the voltage necessary to overcome themagneto-strictive effectof a current required to render incandescent a tungsten filament, issubstantially proportional to the cube of the diameter of the cathode.

In accordance with one feature of my present invention, I have providedelectron discharge devices of the magnetron type utilizing the axialmagneto-strictive effect. The preferred embodiment of my inventioncontains a cathode having a current carrying capacity sufficiently highto conduct currents capable of producing a magnetic field whereby theelectron current may be varied, or even entirely interrupted. I havealso devised new methods and apparatus for utilizing electronic devicesoperating with magneto-strictive current control.

The novel features of my invention will be pointed out with greaterparticularity in the appended claims. A more detailed deseription of myinvention is contained in the following specification taken inconnection with the accompanying drawings in which Fig. 1 is aperspective view of one end of a magnetron embodying my inven tion; Fig.2 is a graph showing the relation between the current traversing thecathode and the space current between the electrodes; Fig. 3 is adiagram of an amplifier system embodying my invention; Fig. 4diagrammatically illustrates a system utilizing my new device for eitherrectifying alterhating current or converting direct to alternatingcurrent; Fig. 5 is a graph showing electrical characteristics of theapparatus shown in Fig. 4; Fig. 6 is a diagram of a radio systemcontaining a magnetron. embodying my invention; and Fig. 7 is a graph ofmagnetic and electrical characteristics of a device such as shown inFigs. 3 and 6.

In devices suitable for use with commercial voltages I have employedtungsten cath ode conductors having a diameter at least several foldgreater than 7 mils at which the control of electron current by themagnetic field of the cathode begins to be efiective. For example, withan applied voltage of about 60 to 80 volts, I have used as cathode atungsten wire of about 40 mils diameter. When the applied voltages areas high as about 1000 volts the cathode diameter should be about 100mils and when the applied voltages are as high as 10,000 volts, a 200mil tungsten conductor is required. \Vhen a cathode material is employedhaving a materially greater or lesser conductivity thantungsten, thecathode diameter, of course, will correspondingly depart from thesedimensions.

To carry the heavy currents into the evacuated container, specialcircuit connections should be provided to obviate cracking of the sealat the cathode terminals as the cathode expands and contracts. Fig. 1shows one end of a tube embodying my invention in which a linear cathode8 is connected to a conductor 9 sealed into the envelope 10. The end ofthe cathode 8 which preferably consists of tungsten is joined by swagingor otherwise to a sleeve of molybdenum, the latter is screw-threadedand'inserted into a threaded socket 11 preferably consisting of copper.A spring consisting of tungsten connects the socket 11 with a similarsocket 12 at the end of the conductor 9. Flexible copper conductors 13connect the sockets 11 and 12 to convey the greater part of the heatingcurrent to the,cathode. A cylindrical anode .14 consisting ofmolybdenum,

copper, tungsten or other suitable material symmetrically surrounds thecathode. This anode may be anchored frietionally to the envelope 10 by acoiled wire 15. As the opposite end of the device is similarlyconstructed and these specific structural features do not in any eventconstitute the present invention, onl apart of the device has beenillustrated. he construction and evacuation of magnetron devices isdescribed in my above-mentioned publication in the J ournal of the,American Institute of Electrical Engineers.

In Fig. 2 the values of electron currents ata constant applied voltageare plotted as ordinates and the cathode currents are plotted asabscissae. Up to a heating current having a value C the electron currentbetween the electrodes 8 and 14 for a given voltage is substantiallyunaffected. An increase of cathode current above 0, produces a rapiddecrease of electron current by causin the electrons to be deflected incurved orbits lying in planes passing through the axis of the cathode.At a value C the electron current has fallen to zero.

When the cathode current varies between the value C, and the electroncurrent will also vary. As shown in Fig. 3 this property of my newdevice may be utilized to amplify a variable current. The input circuit16, 17, which is connected to the cathode terminals, contains a directcurrent source, as for example, a battery 18, and also a source ofalternating current, as for example, the secondary of a transformer 19.The output circuit 20, 21 connected to the electrodes 8 and 14 alsocontains a source of direct current, as for example, a generator 22. Thefigure also includes a transformer 23, having a primary winding fed bythe output circuit 20, 21, but this may be omitted.

In the system shown in Fig. 3 a sufficient current to furnish a fieldcapable of effectively reducing the current in the circuit 20, 21 isfurnished by the battery 18 and superimposed on this is the alternatingcurrent furnished by the transformer 19. The relation between themagnetic fields and the electron current will be better understood byreference to Fig. 7. The magnetic field a out the cathode 8 generated bythedirect current source 18 is represented in this figure by a dottedline Il the ordinates representing magnetic field values and theabscissae time. The superimposed alternating field is represented by thedotted line H,. This gives rise to a resultant variable fieldrepresented by the full line H. When the magnetic field falls below thevalue at which the electron current iscut off, current begins to fiow inthe circuit 20, 21, as represented by the dot and dash curve C of Fig.7. It will be observed that the current rises rapidly to a maximum asthe magnetic field decreases then remains substantially constant, and asthe magnetic field rises the current again falls to zero. During theinterval when the magnetic field is a maximum no current flows in thecircuit 20, 21. In some casesthe direct current source 18 may beomitted. In that case the current in the output circuit 20, 21 will havedouble freuency ofthe current in the circuit 16, 17.

uflicient current should be furnished by the transformer 19 to heat thefilament to incandescence and to generate a controlling field.-

When the system 'shown in Fig. 4 is used fill to rectify alternatingcurrent, then the anodes of the magnetrons 25, 26 are respectivelyconnected to opposite terminals of the secondary of a transformer 27,the cathodes both being connected to a direct current circuit 28, whichin turn is connected to a neutral point of the transformer secondary andcontains a load 29. The cathodes of the magnetrons 25, 26 are suppliedwith current respectively by the secondaries of the transformers 30, 31.The primaries of these transformers are supplied by the mains 32 incommon with the primary of the transformer 27 Except for the magneticfields of the cathode currents, the rectifier system illustratedcorresponds closely to a standard kenotron rectifier system in whichrectification occurs due to unilateral conductivity in avacuum betweenan incandescent cathode and an anode operating below a temperature atwhich electron emission is appreciable. Due to the de flection of theelectrons by the magnetic fields about the cathode in the magnetronrectifiers it is necessary to reduce or cut off the cathode current toenable electrons to flow tothe anode.

Current is alternately interrupted in the cathode circuits of themagnetrons 25, 26 by some suitable device, as for example, a rotatingswitch 33 driven by a motor 34 in synchronism with the alternations ofthe current in the circuit 32. For example, the motor 34 may be suppliedwith energy from the mains 32 by conductors 35 and a transformer 36. Therotating switch shown in the drawing has a. conducting segment and aninsulating segment properly proportioned. During one-half cycle, currentcan flow through the conductors 40, 41 to the cathode of the magnetron26 setting up a magnetic field about the cathode suflicient to cut offspace current flow between cathode and anode. During the other halfeycleno current flows through the cathode but the cathode remains at asufiiciently high temperature to supply electrons for conducting a'current through the tube to the load. The relation between the cathodecurrent and the electron current is best shown by Fig. 5. During theinterval of flow of cathode current (indicated by full lines) nocurrentcould flow between the electrodes through the magnetron since thevoltage of the anode is negative with respect to the cathode, asindicated by the dotted curve, but during the next half wave of zerocathode current when no magnetic field is present, a'space currentflows, as indicated by a full line curve.

When a source of unidirectional current is substituted for the loaddevice 29 (the negative terminal being connecteed to the conductor 28)and the switch 33 is driven at a desired frequencyk, fotr example, by

supplying the motor 34 from an independent source of alternatingcurrent, then impulses of current are delivered through the magnetronsalternately to opposite terminals of the transformer 27, the windingconnected to the magnetronthen becoming the primary and alternating current being delivered from the secondary to the circuit 32. In this caseit is solely the current limiting effect of the magnetic fieldof thecathode current which controls the space current flow through themagnetrons as otherwise current would pass at the same time through bothtubes and no transformation would occur.

Fig. 6 shows a system adapted to furnish oscillating current for radiosending purposes and containing a magnetron embody- 1ng my presentinvention. The cathode 8 is supplied with current from a direct currentsource, represented by a battery 45, a choke coil 46 bein included inthe cathode circuit 47 to exclude high frequency. The input circuit 48,49 which is connected to the electrodes 8, 14, contains a direct currentgenerator 50, preferably shunted by a condenser 51. The output circuit52 which preferably contains a variable inductance 53 is coupled to thecircuit 48 by a transformer 54 and terminates in an antenna The primarywinding of the transformer 54 preferably is shunted by an adjustablecondenser 56. The load circuit 52 is connected to a grounded conductor57 through the cathode. As the load current builds up the magnetic fieldabout the cathode increases until it reaches a value sufiicient tointerrupt the current. Due to this unstable characteristic a surging oroscillating condition is produced, the frequency of the resultingoscillations depending on the capacity and the inductance of the antennacircuit.

What I claim as new anddesire to secure by Letters Patent of the UnitedStates, 1s

1. An electron discharge apparatus comprising means for producing anelectron discharge and for generating a magnetic field substantially atright angles to the axis of said discharge within a range in which saidelectron discharge is varied by said magnetic field, and means forvarying said field.

2. The method of controlling an electron discharge which consists ingenerating in the path of said discharge a magnetic field at rightangles to the axis of said discharge, and varying said field above 'acritical value at which said field is capable of effectively decreasingsaid discharge.

3. The method of controlling an electron discharge between an electronemitting cathode and a cooperating electrode which consists ingenerating a magnetic field at lllt) right angles to. said cathode ofsuflicient said electrodes which consists in reducing the magnitude ofsaid heating current sufficiently to reduce the magnetic field below thecritical value at which electron flow is prevented over periods of timeso short that the temperature and electron emission of said cathode ismaintained sufiiciently high to produce a desired current.

5. The method of operating at a given impressed voltage a magnetronhaving a cathode requiring a heating current of such high magnitude thatthe electron current through said magnetron is decreased by themagnetorstrictive effect which consists in periodically decreasing theheating current of said cathode over intervals so short that the cathodetemperature is maintained during said intervals suflicientlyhigh to emitelectrons supporting the current corresponding to the impressed voltage.

6. An electron discharge device comprising a cathode, an anode locatedabout said cathode, said cathode being adapted both to emit electronsand having an electric conductivity sufliciently great to conduct acurrent of suflicient magnitude to produce a magnetic field which willeffectively reduce an electron current between said electrodes,

7. An electron discharge device comprising ananode and a cathode, saidcathode having electric conductivity and electron emissivity so relatedas to render said cathode capablecf functioning both as a source ofelectrons and as a means for producing a magnetic field havingsufiicient. strength to effectively decrease an electron currentbetweensaid electrodes at agiven impressed voltage.

8. An electron discharge device provided with electrodes for producing aradial electron discharge, one of said electrodes being constructed andarranged to produce a magnetic field at angles to said discharge andhaving sufiicient conductivity to conduct a current the magnetic fieldof which 1s sufficient-ly great to effectively decrease said electrondischarge over a ran e of operating voltages, and means for periodicallydecreasing said field to increase said electron discharge.

9. An electron discharge device comprising means for producing anelectron discharge and for producing a magnetic field at right anglestothe general axis of said discharge, which is of sufiicient value toefi'ectively decrease said discharge.

10. The combination of an energy source, an electron discharge devicecomprising a cylindrical anode, a linear cathode adapted to be heated toincandescence axially disposed within said anode, crcuit connectionsbetween said source-and said electrodes, the current-carrying capacityof said cathode being chosen to'permit conduction of a current ofsufiicient magnitude to generate a magnetic field capable of effectivelysup-- pressing an electron current between said electrodes at thevoltage of said source.

11. The combination of a source of current, an electron discharge devicecompris ing a cathode and an anode arranged in substantially circularsymmetry said cathode being adapted to emit electrons, one of saidelectrodes having a. sufficiently high current-carrying capacity toconduct a current whereb an electron currentbetween said electro es maybe effectively decreased by an axial magneto-strictive effect at thevoltage of said source.

12. An electrical discharge device comprising an exhausted envelope andcooperating electrodes the current-carrying capacity of one of which issufiiciently high to conduct during normal operation a current ca pableof controlling a space current between said electrodes by an axialmagneto-strictive efl'ect.

13. An electrical discharge device comprising cooperating electrodes oneof which is linear, the current-carrying capacity of said linearelectrode bein sufiiciently high to conduct during normal operation acurrent capable of controlling a space current between said electrodesby an axial magneto-strictive effect.

14. An electrical discharge device comprising an exhausted envelope andtwo electrodes only therei the current-carryin" capacity of one oitjwhich is sufficiently 'iigh to conduct duri g normal operation a currentcapable of controlling a space current between said electrodes by anaxial magnetostrictive eflect. v

15. An electrical discharge device containing two electrodes onlyconstituted by a linearcathode, a cooperating anode symmetricallysurrounding said cathode, an enclosing envelope, and means for heatingsaid cathode, the current-carrying capacity of said cathode beingsufiicientl high to permit the heating current for said cathode tocontrol the space current in said device by an axial magneto-strictiveeffect.

16. An electrical discharge device containing (:00 crating electrodesone of which symmetrica 1y surrounds the other, the current carryingcapacity of the surrounded or inner electrode being sufficiently high tocarry during normal operation a current feet. at a given capable ofcontrolling the space current in said device by an axialmagneto-strictive efvoltage impressed upon said electrodes.

17. An electron discharge device which contains a cathode having acurrent carrying capacity so correlated with the electron emissivity ofthe cathode that when the cathode heating current is sufficiently greatto produce a temperature in said cathode at which the electron emissionis substantial then the magnetic tield of'said current exerts an axialmagneto-strictive control upon a space current in said device.

'18. The combination of a work circuit. a current source therein, and anelectron discharge device connected to derive current from said source,said device being provided with an electrode having capacitysufficiently high to conduct a current having a value so related to thevoltage of said source that the space current in said device may becontrolled by the magnetic field of said current by an axialmagneto-strictive effect. I

19. The combination of a work circuit, a source of electric energytherein, an electric discharge device connected to saidcircuit, saiddevice having an electrode s'o constructed and arranged that currentthere through which will render said electrode incandescent alsoproduces a magnetic field capable of controlling space current flowthrough said device by an axial magnetostrictive effect.

20. An electrical discharge apparatus comprising a supply circuit, meansconnected thereto for producing an electron discharge and for exertingan axial magncto-strictive efi'ect sufiicient to control said discharge,and means for varying said effect. 1

21. The combination of a supply circuit, an electron discharge devicecontaining a linear cathode and a cylindrical anode symmetricallysurrounding said cathode, the cathode being proportioned to carry acurrent sufliciently large with respect to the a current carryingvoltage of said circuit to exert control by an axial magueto-strictiveeffect upon an electron current in said device, and means for heatingsaid cathode by a current of suchmagnitude that substantial electronemission is caused in addition to said magneto-strictive effect.

22. An electrical discharge apparatus comprising a work circuit, meansconnected thereto for producing an electron discharge and for exertingan axial magneto-strictive efi'ect suflicient to control said dischargeand means external to said work circuit for varying said effect.

23. The combination of a work circuit, an electron discharge deviceconnected thereto embodying means for producing an axialmagneto-strictive effect for controlling said discharge. a source ofenergy operatively connected to said device, and means for cyclicallyvarying saidmagneto-strictive effeet to produce desired currentvariations in said work circuit.

24. The combination ofan electron discharge device having electrodes oneof which embodies means for producing an axial magneto-strictive effect,a work circuit in series with the electrode capable of exerting saidefi'ect, means for delivering energy to said work circuit, anoscillation circuit connected to said electrodes, and a feed-backconnection between said work circuit and said oscillation circuit.

25. The combination of an electron discharge device having an anode anda cathode which embodies means for producing an axial magneto strictiveeffect, an antenna, series circuit connections between said antenna,said cathode and ground, a source of energy connected to said anode andcathode, an oscillation circuit connected in series between said sourceand said electrodes, and a transformer coupling between said oscillationcircuit and said antenna circuit.

In witness whereof, I have hereunto set my hand this 14th da ofNovember, 1921.

ALl ERT W. HULL.

